What exactly is your goal with this? Do you have a syslog daemon running that listens on 10514 to receive that copy of the data? Also, can you clarify what "doesn't work" means in this case? Does nothing work, or is it just the syslog stream that is not functioning?
It is usually recommended to put that syslog daemon in front of Splunk. Such that the syslog daemon receives the syslog data, writes it to disk and then splunk monitors those files.
Also: why do you have sendCookedData=false for the output to the indexer?